1. Field of the Invention
This invention relates to a linear motion rolling guide unit which includes a slider having endless circulation passages into each of which rolling elements are incorporated and roll to slide the slider on a rail.
2. Description of the Related Art
Such a type of linear motion rolling guide unit is disclosed in JP-H5-164128-A and JP-2003-322151-A, for example. In these examples, rolling elements such as balls or rollers are rotatably held in a slider that comprises a casing and end caps fixed at the opposing ends of the casing. The slider straddles a rail and the rolling elements roll on raceway faces formed on the side faces of the rail, so that the slider is moved relative to the rail.
In a linear motion rolling guide unit comprising a slider straddling the rail as described above, a gap is created between each of the side faces of the rail and the slider. If dust enters the gap between the rail side face and the slider, the dust is dragged into the inside of the slider while the rolling elements roll. The entry of the dust into the slider makes it impossible to maintain a smooth sliding movement of the slider over a long time.
To avoid the entry of dust from the gaps created between the side faces of the rail and the slider, underside seals are secured to the slider to prevent the gaps between the side faces of the rail and the slider from being exposed.
Such underside seals for preventing the entry of dust are secured to the slider as described below. Receiving holes are drilled close to the opposing ends of each of the underside seals in the longitudinal direction. End caps, which are respectively provided on the opposing ends of the casing, have engaging projections each extending out from a portion of each end cap located close to the side face of the rail when the slider straddles the rail. When the engaging projection is fitted into the receiving hole of the underside seal, the underside seal is held in the sliding direction of the slider.
In some operating environments, the aforementioned linear motion rolling guide unit is accompanied by heavy vibration when the slider slides along the rail. For preventing the underside seal from falling away from the slider due to the heavy vibration, the dimensional relationship between the receiving hole in the underside seal and the engaging projection needs to be tightened to eliminate the play of the underside seal.
However, an increase in pressure is necessary to make a tight fitting between the receiving hole and the engaging projection as described above. Specifically, after the engaging projections are inserted into the receiving holes, the underside seal is strongly pressed to fit the engaging projections into the receiving holes.
In many cases, such a linear motion rolling guide unit has end caps formed of resin with a view to reducing weight and cost and the like. When a large external force as described above is applied to the engaging projections formed on a resin-made end cap, a crack may possibly occur in the engaging projections.
For example, in a large-sized linear motion rolling guide unit, when the slider is mounted on the rail, the slider has naturally an increased weight. When the slider with a heavy weight is picked up for transportation, an external force is applied to the underside seal, resulting in equally damage to the engaging projection.
In addition, even if the engaging projection is not damaged in the process of attaching the underside seal, the underside seal is secured in the con in which stress is being applied to the engaging projection, so that the stress causes the engaging projection to gradually deteriorate.
However, as long as the underside seal is attached to the slider, it is impossible to check the degree of deterioration of the engaging projection and the presence/absence of damage thereto. Because of this, until the underside seal actually falls away from the slider, the deterioration of the engaging projection is not found. In other words, it is difficult to replace the end cap or the slider before the underside seal falls off the slider.
In many cases, this results in the replacement of the end cap and the slider after the underside seal has fallen off the slider. If the underside seal falls off the slider, the falling of the underside seal has various adverse effects.
For example, when an apparatus includes a plurality of linear motion rolling guide units arranged in stages in the vertical direction, if a underside seal falls out during operation of the apparatus, the fallen underside seal bites into the slider located under the fallen underside seal, resulting in a chance of failure of the slider and/or a rail.
In an apparatus including a plurality of rails laid on a plane surface, if a underside seal falls between adjacent rails, the operation of the apparatus is required to be halted and then some processes of dismounting the rails and the like need to be performed for removing the fallen underside seal from the apparatus.
Such fallout of an underside seal from a slider as described above gives rise to problems of apparatus failure caused by the fallout from the slider and of stopping the operation of an apparatus in order to remove the fallen underside seal.